netdev - Re: Generic TSO (was Re: [net-next PATCH 0/2] GENEVE/VXLAN: Enable outer Tx checksum by default)

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Message-ID: <56E32966.7090409@solarflare.com>
Date:	Fri, 11 Mar 2016 20:24:06 +0000
From:	Edward Cree <ecree@...arflare.com>
To:	Tom Herbert <tom@...bertland.com>
CC:	Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Generic TSO (was Re: [net-next PATCH 0/2] GENEVE/VXLAN: Enable
 outer Tx checksum by default)

On 11/03/16 20:16, Tom Herbert wrote:
> On Fri, Mar 11, 2016 at 11:59 AM, Edward Cree <ecree@...arflare.com> wrote:
>> On 11/03/16 19:57, Tom Herbert wrote:
>>> On Fri, Mar 11, 2016 at 11:20 AM, Edward Cree <ecree@...arflare.com> wrote:
>>>> Tom,
>>>>
>>>> Are you planning to / working on implementing this?  If not, I might have a
>>>> crack at it; I've talked to our firmware guys and (provisionally) we think
>>>> we can support it in current sfc hardware.
>>>> Or were there any blocking problems raised in the thread?  My understanding
>>>> of the IP ID issue was that it only matters for the inner frame, because
>>>> the rest aren't TCP (so hopefully no-one is doing SLHC on them).  But I may
>>>> have missed something.
>>>>
>>> Right, then the interface would need to just include the offset of the
>>> IP ID. But doesn't this break using LCO with GSO though-- i.e. the
>>> outer checksum and inner checksum still need to be updated per packet
>>> so we need to tell device where outer checksum(s) is.
>> No, outer checksum shouldn't change: IP ID is protected by inner IP header
>> checksum, which device will edit.  No?
> Right, the interface would probably still need offset to the IPv4 hdr?
Yes; I'm assuming the interface could just be "offset to inner IP header",
and the hardware knows well enough what IP and TCP headers look like that
it can figure out the rest (including skipping over options if e.g. ihl>5).
So, do you want to try and implement it or shall I?

-Ed